A dispersion in which metallic copper particles are blended is a general term usually including compositions such as coating agents, paints, pastes, and inks in which metallic copper particles are dispersed in a solvent and additives such as a binder, a dispersing agent, a viscosity controlling agent are further blended when necessary. Such a dispersion is used for various applications, for example, in order to ensure electrical conduction, or in order to give antistatic properties, electromagnetic interference shielding properties, metallic luster, and antibacterial properties, by making use of properties of the metallic copper particles. In addition, in recent years, metallic copper particles whose average particle size is approximately 1 to 200 nm have been used as the metallic copper particles to be blended, so that the application is enlarged in many fields. Specifically, by making use of high conductivity of the metallic copper particles, the metallic copper particles are used to shield transparent members such as cathode ray tubes and liquid crystal displays from electromagnetic interference. Moreover, a technique for forming a fine electrode and a circuit wiring pattern by using metallic copper particles that are a nano material is proposed. This is a technique for applying a dispersion having blended metallic copper particles on a substrate by a coating method such as screen printing and ink jet printing to form a pattern of an electrode or a circuit wiring, and subsequently heating the applied dispersion at a relatively low temperature so that the metallic copper particles are fused. Particularly, this technique is gradually applied to production of a printed circuit board. Further, a simple technique for producing a mirror finished surface attracts attention in design and decoration application because fusing of metallic copper particles easily progresses and metallic luster appears itself even under a mild heating condition.
As metallic copper particles and a dispersion in which the metallic copper particles are dispersed, for example, Patent Literature 1 discloses production of metallic copper particulates by mixing divalent copper oxide with a reducing agent in a medium in the presence of a complexing agent and a protective colloid to reduce the divalent copper oxide, and production of a fluid composition by dispersing the obtained metallic copper particulates in a dispersion medium. Patent Literature 1 describes use of a water-based solvent, a hydrophilic organic solvent, a hydrophobic organic solvent, and the like as the dispersion medium. Patent Literature 2 describes production of a copper colloidal solution containing copper colloidal particles and a polymer pigment dispersing agent by dissolving a copper compound in a solvent, adding the polymer dispersing agent for pigment, and subsequently performing a reduction, and use of a polymer of a comb shaped structure having a pigment-affinitive group in the main chain and/or a plurality of side chains and having a plurality of side chains that form solvated portions as the polymer pigment dispersing agent, and the like.